* {
  margin: 0;
  padding: 0;
}
.box {
  width: 100px;
  height: 100px;
  position: absolute;
}
.b0x1 {
  top: 20px;
  left: 20px;
  background-color: #f00;
  z-index: 1;
}
.box2 {
  top: 40px;
  left: 40px;
  background-color: #00f;
  z-index: 2;
}
